Many articles, such as optical media, including DVDs (digital versatile discs) and CDs (compact discs), as well as documents such as passports, personal identification, artwork and others are frequently considered valuable. Advancements in various printing and other technologies have improved the ability to incorporate identification information into many of these articles. As a result, schemes for including information have become increasingly sophisticated. For example, security marking schemes now include various embodiments of logos, bar codes and digital watermarks. However, some items, such as optical media present challenges to existing technology, and require further advanced schemes.
An example of an advanced security marking is a digital watermark. Digital watermarks are known, and increasingly used in a variety of applications. Watermarks, or signatures, are typically produced by using semantic information of the item to be protected. For example, digital watermarks may include alphanumeric characters, physical features, etc. or other related information (e.g. ownership information). These signatures, or watermarks, are typically kept with, or incorporated covertly or overtly into the item to be protected. For example, a watermark may be printed within the substrate of a negotiable instrument that includes information regarding the value and the originator of the instrument.
Various digital watermarking techniques are known for both still and video images. For example, reference may be had to U.S. Pat. No. 6,343,138 B1, entitled “Security Documents with Hidden Digital Data”, issued Jan. 29, 2002. This patent discloses, among other things, embedding a digital watermark into a video signal or a still image.
Some of the known techniques include separately coding the image and a watermark image using a pseudo random number generator and a discrete cosine transform (DCT) to form coded blocks, one of the image to be watermarked and the other of the watermark itself. The DCT coefficients representing the coded watermark block and the coded image block are then added together to form a combined block thus digitally watermarking the image.
Reference may also be had to U.S. Pat. No. 6,037,984, entitled “Method and Apparatus for Embedding a Watermark into a Digital Image or Image Sequence,” by Isnardi et al., issued Mar. 14, 2000. This patent discloses watermarking an image or sequence of images using a conventional DCT unit and quantizer. The patent discloses generating an array of quantized DCT coefficients and watermarking the array by selecting certain ones of the DCT coefficients and replacing them with zero values. The masked array is further processed by a watermark inserter that replaces the zero valued coefficients with predefined watermark coefficients to form a watermarked array of DCT coefficients, that is, a watermarked image.
Techniques for embedding a watermark are typically dependent upon the substrate, and the existing technology for marking the substrate. For example, one technology that has been useful in the improvement of the quality of still images is printing of images with UV curable ink. Inks, which require UV exposure to cure, are generally considered to be superior to traditional solvent-based inks for reasons that include the versatile application of the ink. Ease of application has resulted from, among other things, the solid composition of the ink, the ink can be laid down heavily, and cured almost instantaneously. Other advantages include increased wear, and better color control. Although printing with UV curable ink can provide for improved printed images over conventional solvent-based inks, it does not lend itself well to some marking applications. For instance, printing with UV curable ink may improve the quality of a marking on the backside of a CD, however, addition of such ink would impede the functionality if deposited on the read side.
It is also well known to apply fluorescent coatings for identification. Reference in this regard may be had to U.S. Pat. No. 3,513,320, entitled “Article Identification System Detecting Plurality of Colors Disposed on Article,” issued May 19, 1970, by Weldon.
In addition, invisible ink may used to provide concealed markings. For example, reference may be had to U.S. Pat. No. 6,203,069, entitled “Label Having an Invisible Bar Code Applied Thereon,” issued May 8, 2001. Additionally, U.S. Pat. No. 6,138,913, entitled “Security Document and Method Using Invisible Coded Markings,” issued Oct. 31, 2000. These patents disclose variations of invisible bar codes, wherein invisible ink is used in a bar code.
It is further known that fluorescing materials may be incorporated into various materials, including polymeric materials. For example, reference may be bad to U.S. Pat. No. 6,120,902 “Luminescent Article with Protective Coating and Manufacture” issued Sep. 19, 2000. This patent discloses the use of luminescent materials to create a luminescent article, the coating of the materials, and the curing of the coating with radiation. Although such combinations of materials may provide some advantages, the combination of luminescent materials and a coating may not be adequate for some sophisticated marking schemes.
Further, it is known to apply radiation sensitive coatings to objects for imaging by exposure to light of various wavelengths. Furthermore, the use of photo-generated acids in combinations with acid sensitive color forming compounds is well known. For example, refer to U.S. Pat. No. 5,436,115, entitled “Systems for the Visualization of Exposure to Ultraviolet Radiation,” issued Jul. 25, 1995. Likewise, invisible fluorescent images may be developed using similar technology and acid sensitive fluorescent dyes, such as those reported in “Positive and negative fluorescent imaging induced by naphthalimide polymers” by He Tian, Jiaan Gan, Kongchang Chen, Jun He, Qun Liang Songb and Xiao Yuan Houb, Journal of Materials Chemistry 2002, 12, 1262–1267.
In addition, reference may be bad to U.S. Patents directed towards optical storage systems. For example, U.S. Pat. No. 5,549,953, entitled “Optical Recording Media Having Optically-Variable Security Properties” by Li Li, issued Aug. 27, 1996, discloses a technique to prevent counterfeiting of various substrates through introducing thin film structures having optically variable security properties and encoded optical data. This patent discloses the use of a multilayer interference coating, which may be characterized by optically variable properties. However, the teachings of this patent can be difficult to implement in a high volume optical media production environment.
Another U.S. Pat. No. 5,510,163, entitled “Optical Storage Media Having Visible Logos”, by Sullivan, et al., issued on Apr. 23, 1996. This patent also discloses a technique to prevent counterfeiting of optical storage media, specifically through producing a visible logo on the read side of the substrate. This patent discloses deposition processes for production of a logo coating, such as evaporation or sputtering, chemical vapor deposition, and others. The logos are prepared by exposing either some or all of the layers through a mask. As with U.S. Pat. No. 5,549,953, the teachings of this patent may be difficult to implement in a high volume production environment.
A need exists to provide enhanced identification, authentication and encoding capabilities for various articles of manufacture, including media containing optically readable information. More specifically, a need exists to rapidly produce images, text, or other optically encoded information on the read side of optical media. Further more, the method should not interfere with the performance of data readout from the optical media.